Positional identification of fluorine in methyl per-O-acetyl-x-deoxy-x-fluoro-alpha-D-hexopyranosides by electron impact and chemical ionisation mass spectrometry.

Fully acetylated methyl x-deoxy-x-fluoro-alpha-D-glucopyranosides have been studied using electron impact and ammonia chemical ionisation mass spectrometry. Mass analysed metastable ion kinetic energy spectroscopy (MIKE), collisional activation (CID), and accelerated voltage scanning have been used to evaluate complete fragmentation schemes. Characteristic differences in the fragmentation of positional isomers were noted on analysis of the spectra, and these make it possible to determine the location of fluorine in the molecules studied. Collisionally activated fragmentation of [M-OCH3]+ ions, produced by electron impact, provides an alternative method for localisation of the fluorine atoms. To the contrary, MIKE and CID spectra of [M + NH4]+ cluster ions produced by chemical ionisation did not afford such structural information.